Hybrid electric vehicle controller and method

ABSTRACT

Embodiments of the present invention provide a controller for a hybrid electric vehicle having an engine, electric propulsion means powered by energy storage means and electric generator means operable to be driven by the engine to recharge the energy storage means, the controller being operable to: receive a signal indicative of a required hybrid driving mode; receive a signal indicative of a state of charge of the energy storage means; determine which of a plurality of powertrain operating modes is appropriate for vehicle operation at a given moment, the powertrain operating modes including an engine charging mode in which the engine drives the generator means to recharge the energy storage means and an electric vehicle (EV) mode in which the engine is switched off and the electric propulsion means is operable to develop drive torque to drive the vehicle; and cause the powertrain to assume the appropriate powertrain operating mode and the required hybrid driving mode, wherein the controller is operable to determine which of the plurality of powertrain operating modes is appropriate for vehicle operation in dependence at least in part on the signal indicative of the instant state of charge of the energy storage means and a reference value of state of charge, the controller being operable to set the reference value of state of charge to one of a plurality of different respective values in dependence on the signal indicative of the required hybrid driving mode.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/910,814, filed Feb. 8, 2016, which itself is a 35 U.S.C. § 371national stage application of PCT Application No. PCT/EP2014/067752,filed on Aug. 20, 2014, which claims priority from Great Britain PatentApplication No. 1314990.1 filed on Aug. 21, 2013, the contents of whichare incorporated herein by reference in their entireties. Theabove-referenced PCT International Application was published in theEnglish language as International Publication No. WO 2015/024971 A2 onFeb. 26, 2015.

TECHNICAL FIELD

The present invention relates to controllers for hybrid electricvehicles. In particular embodiments of the invention relate tocontrollers for hybrid electric vehicles operable in a parallel mode.

BACKGROUND

It is known to provide a hybrid electric vehicle having an internalcombustion engine operable to provide drive torque to drive the vehicleand an electrical propulsion motor operable to provide drive torque whenthe vehicle is operated in an electric vehicle (EV) mode. A vehiclecontrol system determines when to switch the internal combustion engineon or off, and when to open or close a clutch KO between the engine anda transmission. In some vehicles the electric propulsion motor isintegrated into the transmission.

It is also known to provide an electric machine as a starter forcranking the engine when an engine start is required. Known startersinclude belt-integrated starter/generators. Such devices are operable aselectrical generators driven by the engine as well as a starter. Thevehicle may include a belt integrated starter generator in addition to astarter for starting the engine, in some embodiments.

SUMMARY OF THE INVENTION

Embodiments of the invention may be understood with reference to theappended claims.

Aspects of the present invention provide a control system, a vehicle anda method.

In one aspect of the invention for which protection is sought there isprovided a controller for a hybrid electric vehicle having an engine,electric propulsion means powered by energy storage means and electricgenerator means operable to be driven by the engine to recharge theenergy storage means, the controller being operable to:

-   -   receive a signal indicative of a required hybrid driving mode;    -   receive a signal indicative of a state of charge of the energy        storage means;    -   determine which of a plurality of powertrain operating modes is        appropriate for vehicle operation at a given moment, the        powertrain operating modes including an engine charging mode in        which the engine drives the generator means to recharge the        energy storage means and an electric vehicle (EV) mode in which        the engine is switched off and the electric propulsion means is        operable to develop drive torque to drive the vehicle; and cause        the powertrain to assume the appropriate powertrain operating        mode and the required hybrid driving mode,        wherein the controller is operable to determine which of the        plurality of powertrain operating modes is appropriate for        vehicle operation in dependence at least in part on the signal        indicative of the instant state of charge of the energy storage        means and a reference value of state of charge, the controller        being operable to set the reference value of state of charge to        one of a plurality of different respective values in dependence        on the signal indicative of the required hybrid driving mode.

Embodiments of the present invention have the advantage that theoperating mode of the powertrain at a given moment in time may beinfluenced by adjustment of the reference value of the state of chargedepending on the selected hybrid driving mode. Thus, in some embodimentsthe controller may be configured to favour operation of the powertrainin the EV mode when a particular driving mode is selected. Thus if auser wishes to enjoy vehicle operation in EV mode more than a mode inwhich the engine is switched on, the user may select a correspondinghybrid driving mode.

It is to be understood that reference to an instant state of charge isto be understood to mean a prevailing or current state of charge of theenergy storage means. The instant state of charge may be the mostrecently available measured value of state of charge of the energystorage means in some embodiments.

The engine may be an internal combustion engine. The engine may bepetrol fired or diesel fired. Other arrangements are also useful.

The controller may be operable to determine the appropriate powertrainoperating mode in dependence at least in part on a deviation of thesignal indicative of the instant state of charge from the referencevalue of state of charge.

It is to be understood that in some embodiments the controller may bearranged to promote charging of the energy storage means to a higherstate of charge when the powertrain is in the engine charging mode, thusfavouring operation of the powertrain in the EV mode for longer periodswhen the engine is switched off.

The controller may be operable to determine which of the powertrainoperating modes is appropriate at a given moment in time according to avalue of a cost function for each powertrain operating mode, the valueof the cost function being determined at least in part by reference tothe signal indicative of the instant state of charge and the referencevalue of state of charge of the respective powertrain operating modes.

Optionally, the value of the cost function of each powertrain operatingmode is determined at least in part in further dependence on at leastone selected from amongst a rate of fuel consumption of the vehicle, arate of emission of a gas by the vehicle and an amount of noisegenerated by the vehicle.

The controller may be configured to determine the required powertrainoperating mode according to a feedback Stackelberg equilibrium controloptimisation methodology.

Such a methodology is known, and may be understood for example byreference to UK patent application GB1115248.5.

In some embodiments, the cost function is responsive at least in part toa rate of fuel consumption of the vehicle, a rate of emission of a gasby the vehicle and/or a deviation of a state of charge of the energystorage means from the reference value.

The controller may be arranged to receive a signal indicative of therequired hybrid driving mode from a user.

That is, the user may input a signal indicative of the required hybriddriving mode.

Optionally, the hybrid driving modes include a first driving modefavouring prolonged operation in EV mode, and a second driving modefavouring a reduction in fuel consumption, wherein the value ofreference state of charge in the first driving mode is higher than thatin the second driving mode.

The first mode may correspond to a selectable electric vehicle (SEV)mode. The second mode may correspond to a general or default hybridelectric vehicle (HEV) driving mode. In embodiments, other modes may beavailable and/or useful.

Advantageously, when the powertrain is in the EV powertrain mode thecontroller may be operable to cause the powertrain to assume the enginecharging powertrain mode in dependence at least in part on driver torquedemand. If the vehicle is in the first mode and the powertrain is in theEV powertrain mode, the controller may be arranged to cause thepowertrain to switch from the EV mode to the engine charging powertrainmode only above a threshold value of driver torque demand that is higherthan that when the vehicle is operating in the second mode.

Advantageously, when the powertrain is in the engine charging operatingmode the controller may be configured to cause the generator means toapply a greater charging load to the engine when the vehicle is in thefirst driving mode compared with the second driving mode.

This feature has the advantage that, because the energy storage means ischarged more aggressively in the first mode, the state of chargeincreases more quickly, enabling the vehicle to spend a greater amountof time in the EV powertrain operating mode.

Optionally when the powertrain is in the EV operating mode thecontroller is operable to cause the engine to switch on when vehiclespeed exceeds a prescribed value, the prescribed value being higher whenthe vehicle is operating in the first mode relative to the second mode.

The prescribed vehicle speed for engine start may be gradient dependent.That is, the threshold may be greater when the vehicle is descending ahill compared with travel over flat terrain, or uphill. The speed mayincrease with increasing downhill gradient steepness.

The engine may be switched on to provide drive torque in the case of aparallel hybrid vehicle, or so that the powertrain can assume the enginecharging mode in the case of a parallel hybrid electric vehicle or aseries hybrid electric vehicle.

Optionally, when the controller causes the vehicle to operate in thefirst mode or the second mode the controller causes the engine to turnon in dependence at least in part on an amount by which an acceleratorpedal is depressed.

If the accelerator pedal is not depressed, or depressed by less than athreshold amount, the controller may cause the powertrain to remain inthe EV mode. Thus if a vehicle speed increases above a turn-on thresholddue to coasting downhill, the vehicle may remain in the EV mode.

Optionally the state of charge of the energy storage means is permittedto take a value from a prescribed absolute minimum state of charge to aprescribed soft minimum value greater than the prescribed absoluteminimum state of charge only when the vehicle is operating in the firsthybrid operating mode or upon vehicle initialisation.

The magnitude of the interval from the prescribed absolute minimum stateof charge to the prescribed soft minimum value may be approximately 10%of the magnitude of the interval from the prescribed absolute minimumstate of charge to a prescribed absolute maximum state of charge.

This has the benefit that the powertrain is more likely to operate inthe EV mode when the driver selects the first mode because the intervalof state of charge values below the soft minimum value (that is, in theso-called ‘reserved’ interval) will normally be available for use. Thereserved interval may be used automatically upon vehicle initialisationthus providing a smooth vehicle departure from rest. Once the vehiclehas operated in the reserved interval, the controller may subsequentlyinhibit vehicle operation in said reserved interval when the state ofcharge value increases above the prescribed soft minimum value. Thishelps to some extent to ensure that the driver does not experienceprolonged periods when the engine is on and/or periods where a greatercharging load to the engine is applied when the vehicle is no longeroperating in the first mode.

The controller may be operable to cause the engine to be drivablycoupled to one or more wheels of the vehicle in addition to the electricpropulsion means.

Thus the controller may be suitable for controlling a parallel hybridvehicle.

The controller may be operable to cause the engine to deliver drivetorque when the powertrain is operated in the engine charging mode.

The controller may be operable to cause the powertrain to operate in aparallel boost mode in which the engine delivers drive torque inaddition to the electric propulsion means.

In a further aspect of the invention for which protection is soughtthere is provided a hybrid electric vehicle powertrain comprising acontroller according to a preceding aspect.

Optionally, the electric generator means and the electric propulsionmeans are each provided by an electric machine.

The controller may be operable to cause the electric machine to beoperated as a propulsion motor or a generator.

The generator means may comprise an electric generator and the electricpropulsion means may comprise a propulsion motor.

In a further aspect of the invention there is provided a hybrid electricvehicle comprising a controller or a powertrain according to a precedingaspect.

The vehicle may be operable in a parallel mode in which the enginedelivers drive torque to the powertrain.

The vehicle may be operable in a series mode in which the engine drivesthe generator means to develop charge to recharge the battery or powerthe propulsion motor whilst the propulsion motor delivers drive torqueto the powertrain.

In a further aspect of the invention for which protection is soughtthere is provided a method of controlling a hybrid electric vehiclehaving an engine, electric propulsion means powered by energy storagemeans and electric generator means operable to be driven by the engineto recharge the energy storage means, the method comprising:

-   -   receiving a signal indicative of a required hybrid driving mode;    -   receiving a signal indicative of a state of charge of the energy        storage means;    -   determining which of a plurality of powertrain operating modes        is appropriate for vehicle operation at a given moment, the        powertrain operating modes including an engine charging mode in        which the engine drives the generator means to recharge the        energy storage means and an electric vehicle (EV) mode in which        the engine is switched off and the electric propulsion means is        operable to develop drive torque to drive the vehicle; and        causing the powertrain to assume the appropriate powertrain        operating mode and the required hybrid driving mode,    -   the method comprising determining which of the plurality of        powertrain operating modes is appropriate for vehicle operation        in dependence at least in part on the signal indicative of the        instant state of charge of the energy storage means and a        reference value of state of charge, and setting the reference        value of state of charge to one of a plurality of different        respective values in dependence on the signal indicative of the        required hybrid driving mode.

In one aspect of the invention for which protection is sought there isprovided a computer readable medium carrying computer program code forcontrolling a vehicle to carry out a method according to a precedingaspect.

Within the scope of this application it is envisaged that the variousaspects, embodiments, examples, features and alternatives set out in thepreceding paragraphs, in the claims and/or in the following descriptionand drawings may be taken independently or in any combination. Featuresdescribed with reference to one embodiment are applicable to allembodiments, unless there is incompatibility of features.

For the avoidance of doubt, it is to be understood that featuresdescribed with respect to one aspect of the invention may be includedwithin any other aspect of the invention, alone or in appropriatecombination with one or more other features.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to theaccompanying figures in which:

FIG. 1 is a schematic illustration of a hybrid electric vehicleaccording to an embodiment of the present invention; and

FIG. 2 illustrates operation of the vehicle of FIG. 1 in a generalhybrid electric vehicle (HEV) driving mode;

FIG. 3 illustrates operation of the vehicle of FIG. 1 in a selectableelectric vehicle (SEV) driving mode; and

FIG. 4 is a table illustrating changes in vehicle behaviour whenoperating in the SEV mode compared with operation in the HEV mode.

DETAILED DESCRIPTION

In one embodiment of the invention a hybrid electric vehicle 100 isprovided as shown in FIG. 1. The vehicle 100 has an engine 121 coupledto a belt integrated starter generator (BISG) 123B. The BISG 123B mayalso be referred to as a belt integrated (or belt mounted) motorgenerator and is operable to crank the engine 121 when starting isrequired. In addition or instead, a dedicated starter motor may beprovided. In some embodiments therefore, a BISG may be provided but aseparate starter motor is employed for starting the engine 121. Theengine 121 is coupled in turn to a crankshaft-integratedstarter/generator (CIMG) 123C by means of a clutch 122. The clutch 122may also be referred to as a KO clutch 122.

The CIMG 123C is integrated into a housing of a transmission 124 whichis in turn coupled to a driveline 130 of the vehicle 100 thereby todrive a pair of front wheels 111, 112 and a pair of rear wheels 114, 115of the vehicle 100. The driveline 130 in combination with thetransmission 124, CIMG 123C, clutch 122, engine 121 and BISG 123B may beconsidered to form part of a powertrain 131 of the vehicle 100. Wheels111, 112, 114, 115 arranged to be driven by the driveline 130 may alsobe considered to form part of the powertrain 131.

It is to be understood that other arrangements are also useful. Forexample the driveline 130 may be arranged to drive the pair of frontwheels 111, 112 only or the pair of rear wheels 114, 115 only, or to beswitchable between a two wheel drive mode in which the front or rearwheels only are driven and a four wheel drive mode in which the frontand rear wheels are driven.

The BISG 123B and CIMG 123C are arranged to be electrically coupled to acharge storage module 150 having a battery and an inverter. The module150 is operable to supply the BISG 123B and/or CIMG 123C with electricalpower when one or both are operated as propulsion motors. Similarly, themodule 150 may receive and store electrical power generated by the BISG123B and/or CIMG 123C when one or both are operated as electricalgenerators. In some embodiments, the CIMG 123C and BISG 123B may beconfigured to generate different electrical potentials to one another.Accordingly, in some embodiments each is connected to a respectiveinverter adapted to operate at the corresponding potential of the CIMG123C or BISG 123B. Each inverter may have a respective batteryassociated therewith. In some alternative embodiments the CIMG 123C andBISG 123B may be coupled to a single inverter which is adapted toreceive charge from the CIMG 123C and BISG 123B at the respectivepotentials and to store the charge in a single battery. Otherarrangements are also useful.

As noted above, the BISG 123B has an electric machine 123BM that isdrivably coupled to a crankshaft 121C of the engine 121 by means of abelt 123BB. The BISG 123B is operable to provide torque to thecrankshaft 121C when it is required to start the engine 121 or when itis required to provide torque-assist to the driveline 130 as discussedin further detail below.

The vehicle 100 has a vehicle controller 140 operable to command apowertrain controller 141PT to control the engine 121 to switch on oroff and to generate a required amount of torque. The vehicle controller140 is also operable to command the powertrain controller 141PT tocontrol the BISG 123B to apply a required value of positive or negativetorque (operating as a propulsion motor or a generator) to the engine121. Similarly, the vehicle controller 140 may command the CIMG 123C toapply a required value of positive or negative torque (again operatingas a propulsion motor or a generator) to the driveline 130 via thetransmission 124.

The vehicle has an accelerator pedal 171 and a brake pedal 172. Theaccelerator pedal 171 provides an output signal to the vehiclecontroller 140 indicative of an amount by which the pedal 171 isdepressed. The vehicle controller 140 is arranged to determine theamount of driver demanded torque based on the accelerator pedal positionand one or more other vehicle parameters including engine speed W.

The vehicle 100 of FIG. 1 is operable by the vehicle controller 140 inan electric vehicle (EV) mode in which the clutch 122 is open and thecrankshaft 121C is stationary. In EV mode the CIMG 123C is operable toapply positive or negative torque to the driveline 130 via thetransmission 124. Negative torque may be applied for example whenregenerative braking is required under the control of a brake controller142B.

The powertrain 131 is operable in one of a plurality of parallel modesin which the engine 121 is switched on and the clutch 122 is closed. Theparallel modes include a ‘parallel boost’ mode in which the CIMG 123C isoperated as a motor to provide drive torque to the driveline 130 inaddition to the torque provided by the engine 121. In the presentembodiment the powertrain 131 is operated in the parallel boostconfiguration when the amount of driver demanded torque exceeds themaximum torque available from the engine 121. The amount of additionaltorque available from the CIMG 123C may be determined in dependence onthe vehicle configuration as described in more detail below. It is to beunderstood that the feature of torque boost increases the availabledrive torque beyond that which is available from the engine 121 alone.

The parallel modes also include a parallel torque filling mode and aparallel torque assist mode. The parallel torque filling mode is a modein which the CIMG 123C delivers drive torque to the driveline 130 inaddition to the engine 121 in order to meet driver demand for torquemore quickly than if the engine 121 alone delivers drive torque. Torquefilling provides the benefit that driver torque demand may be satisfiedmore quickly, improving a responsiveness of the vehicle to an increasein torque demand.

In the present embodiment torque filling is implemented when a rate ofincrease of driver torque demand relative to the amount of torquedelivered by the engine 121 exceeds a prescribed value. Once drivertorque demand has been satisfied, the amount of torque delivered by theCIMG 123C decreases as the amount of torque delivered by the engine 121increases to meet driver demand substantially entirely, without arequirement for additional torque from the CIMG 123C.

In the torque-assist parallel mode the CIMG 123C provides steady-statedrive torque in addition to the engine 121 in order to relieve loadingon the engine 121. This may assist in reducing fuel consumption.Torque-assist may be considered to be distinct from ‘torque filling’,the latter being employed in a transient manner when an increase indrive torque is required.

The powertrain 131 may alternatively be operated in a parallel rechargemode in which the CIMG 123C is driven as a generator by the engine 121to recharge the charge storage module 150.

In the present embodiment, the vehicle 100 is also operable in one of aplurality of hybrid operating modes. The hybrid operating modes includea default hybrid electric vehicle (HEV) operating mode and auser-selectable EV hybrid operating mode, referred to herein as a‘selectable EV operating mode’ (SEV operating mode). The SEV operatingmode is selected by a user by means of SEV selector button 145accessible to a driver whilst driving. When depressed, the SEV button145 illuminates to confirm the SEV operating mode has been selected.

In the present embodiment the vehicle 100 is also operable in aselectable hybrid inhibit (SHI) hybrid operating mode in which thecontroller 140 causes the engine 121 to latch in the on condition, andin a command shift or ‘tip shift’ (TIP) hybrid operating mode.

Whether the vehicle is operating in the HEV hybrid operating mode, theSEV hybrid operating mode, the SHI hybrid operating mode or the TIPoperating mode the controller 140 is configured to determine in whichavailable powertrain mode the powertrain 131 should be operated independence on an energy optimisation strategy that employs game theory.It is to be understood that in the SHI hybrid operating mode the EV modeis not available since the engine 121 is latched in the on condition.The controller 140 is configured to take this factor into account indetermining the required powertrain mode, however in the presentembodiment the controller 140 still employs the same energy optimisationstrategy. Other arrangements are also useful.

The non-cooperative approach of game theory is applied by considering amulti-stage game played by the following two players: a) a first player,the driver, represented by a discrete set of load sites (for examplewheel torque, wheel speed and gear selected), covering the powertraincapability, and b) a second player, the powertrain, represented by adiscrete set of operating modes.

The first player is interested in minimizing a cost functional while thesecond player is interested in maximizing the cost functional. The costfunctional is formed as a sum of incremental cost values over a finitehorizon.

In respect of the embodiment of FIG. 1 the cost functional of the gameis based on the following incremental cost function L related to thecontrol action, u, the state vector, x, and the operating variable, w:

L(x,u,w)=α×Fuel(u, w)+β×NOx(u,w)+μ×[SoC_(SetPoint)−(x−ΔSoC(u,w))]²+γ×G(w)

where u∈U is the control action (U is the set of powertrain modes inthis case which include the parallel boost mode and parallel rechargemode), x∈X is the state vector (X is the set of discretised high voltagebattery SoC (state of charge) values in this case) and w∈W is the vectorof operating variables which is also referred to as the load site(discretised wheel speed, wheel torque and gear selected in this case).In the above equation, Fuel denotes engine fuel consumption, NOx denotesengine NOx emission mass flow rate, SoC_(SetPoint) denotes the desiredSoC set-point at the end of the cycle, ΔSoC(u, w) denotes the deviationof SoC resulting from a defined control action at a given load site.

Here G denotes a positive Gaussian function with the centre at thecentre of mass of a defined drive cycle, introduced to focus theoptimization on specific load sites.

In the present embodiment, the value of SoC set-point (which may bereferred to also as a target value or a reference value) is changed independence on whether the vehicle 100 is operated in the SEV mode, theHEV mode or the TIP mode. The SoC set-point may also be changed independence on transmission operating mode. The value of SoC set-point isset to a higher value for operation in the SEV mode, TIP mode andtransmission sport operating mode (when in the HEV mode) compared withoperation in the HEV mode in the drive transmission operating mode inorder to promote charging of the charge storage module 150. In thepresent embodiment, if the vehicle 100 is operated in the SEV mode, TIPmode or if the transmission 124 is operated in the sport mode whilst inHEV mode, the value of SoC set-point (that is, Game Theory setpoint,also referred to as target value or reference value) is set to 65%(other values are also useful) whilst if the vehicle 100 is operated inthe HEV mode (with the transmission in the drive mode) the value of SoCset-point is set to 52%. Other values are also useful. Similarly, othervalues of SoC set-point whilst operating in various hybrid andtransmission operating modes are also useful. The fact that the value ofSoC set-point is set to a higher value in the SEV mode causes thecontroller 140 to tend to charge the charge storage module 150 to highervalues of state of charge (SoC). For operation in the SHI and TIP hybridmodes, the SoC set-point may be set to the same value as the HEV mode,or to any other suitable value.

FIG. 2 and FIG. 3 are graphical illustrations of the manner in which thecontroller 140 causes the vehicle 100 to operate when the HEV and SEVdriving modes are selected, respectively. The figures show state ofcharge of the charge storage module 150 along a horizontal axis. Thecontent of the figures will now be discussed.

In order to promote operation of the vehicle 100 in the EV mode when thevehicle is in the SEV mode, the controller 140 is configured toimplement the following measures:

-   (a) When in SEV mode, the rate of charging of the charge storage    module 150 when the powertrain is in the parallel recharge mode is    increased relative to that employed in the HEV mode. The vehicle 100    is therefore able to spend longer periods of time in the EV mode for    a given drivecycle, satisfying the user requirement to increase the    time in which the powertrain 131 spends in the EV powertrain mode.-   (b) When in SEV mode, the engine 121 is forced to turn on at a    higher engine-on threshold vehicle speed compared with operation in    the HEV mode. In the present embodiment the engine 121 is forced to    turn on when vehicle speed exceeds 35 mph and the accelerator pedal    171 is depressed, compared with 30 mph in the HEV mode. Other values    are also useful. This feature reduces the chances of the engine 121    being switched on when a user is attempting to maintain a speed of    30 mph, for example when driving on a road having a speed limit of    30 mph. Thus the engine-on threshold speed may be set to a value    exceeding that of a prevailing speed limit. If the accelerator pedal    171 is not depressed, the engine 121 may remain off even though    vehicle speed exceeds the engine-on threshold. This is so as to    avoid switching the engine 121 on unnecessarily when the engine-on    threshold is exceeded, for example when coasting downhill.-   (c) If the engine 121 switches on whilst the vehicle 100 is    cornering in SEV mode, the controller 140 allows the engine 121 to    switch off if the energy optimisation strategy determines this    should be undertaken. In contrast, if the vehicle is operating in    the HEV mode and the engine 121 switches on during cornering, the    engine 121 is latched in the on state until the corner has been    negotiated and the value of lateral acceleration falls below a    prescribed value, indicative that the vehicle is no longer    cornering, for a prescribed period of time, such as 5 s or more.-   (d) If the transmission 124 of the vehicle 100 is placed in the park    or neutral mode and a minimum allowable state of charge of the    charge storage module 150 has been reached or is reached, the energy    storage module 150 is charged at the maximum allowable rate of    charge whenever the engine 121 develops sufficient power (or    operates at a sufficiently high speed) to enable the CIMG 123C to be    driven as a generator.

In some embodiments charging may not be performed if the engine isoperating at idle speed, however if the engine speed is subject to anincrease in response to depression of an accelerator pedal 171 by adriver the controller 140 takes the opportunity to recharge the energystorage module 150 by means of the CIMG 123C at as high a rate as can beachieved. In some embodiments the controller 140 may cause a speed ofthe engine 121 to increase in order to allow charging of the chargestorage module 150.

-   (e) If the SoC of the charge storage module 150 falls below a first    prescribed value (which may be referred to as a minimum SoC or soft    minimum limit) when the vehicle is operating in the SEV hybrid mode,    the engine 121 is latched on and the CIMG 123C is operated as a    generator to recharge the charge storage module 150 at the fastest    allowable rate. In contrast, in the HEV hybrid mode the controller    140 causes the CIMG 123C to recharge at a rate determined in    dependence on the energy optimisation strategy. The controller 140    suspends application of game theory to determine the preferred    powertrain operating mode when the SoC falls below the first    prescribed value. In the present embodiment the first prescribed    value is around 39% although other values are also useful.

It is to be understood that in known hybrid electric vehicles andelectric vehicles, a battery for storing charge is only permitted tovary its SoC between prescribed values (which may be referred to as hardlimits) that lie within the absolute maximum and minimum states ofcharge in order to prevent deterioration in battery life due toexcessively high and low charge states. In the present embodiment theminimum allowable battery SoC is 35% whilst the maximum allowable SoC is70%. Other values are also useful.

-   (f) The vehicle 100 may not operate in the HEV hybrid mode if the    SoC falls below a second prescribed value (or prescribed soft    minimum value) which may be greater or less than the abovementioned    first prescribed value. The SoC interval from the absolute minimum    SoC to the second prescribed value is reserved specifically for the    SEV hybrid mode. This will enable vehicle ‘pull-away’ in the EV mode    upon initialisation of the vehicle 100. Specifically, the SoC is    permitted to be less than the second prescribed value if the SEV    hybrid mode is selected by the driver or the vehicle 100 has just    been initialised. If the SoC assumes a value that is less than the    prescribed second value, the SoC is no longer permitted to be less    than said second prescribed value if the SEV hybrid mode is not    selected or deselected and the SoC subsequently assumes a value    greater than the second prescribed value. The SoC interval from the    absolute minimum SoC to the second prescribed value may be    approximately 10% of the permitted SoC interval (that is, the    interval from the absolute minimum SoC to the absolute maximum SoC).    Other values are also useful.

In the present embodiment, if the SoC of the charge storage module 150reaches a value below a prescribed engine start SoC value, thecontroller 140 forces the powertrain to assume the parallel rechargemode until the SoC of the charge storage module 150 exceeds a prescribedminimum engine stop SoC value. Once the SoC exceeds the minimum enginestop SoC value the powertrain 131 may resume operation in the EV mode ifthe controller 140 determines this is the optimum mode according to theenergy optimisation strategy. If the powertrain 131 resumes operation inthe EV mode once the SoC exceeds the prescribed minimum engine stop SoCvalue following an engine start due to the SoC falling below the enginestart SoC value, the minimum engine stop SoC value is incremented by aprescribed increment amount. In the present embodiment, the prescribedincrement amount is higher when operating in SEV mode compared with HEVmode although in some embodiments the increment amounts may besubstantially equal. This feature has the effect that when the engine121 is next started, it must charge the energy storage module 150 to ahigher SoC before the engine 121 may be switched off, increasing theavailable charge for operation in EV mode.

In the present embodiment, when operating in HEV mode the prescribedincrement amount is 2% each time the engine is stopped as soon as theSoC reaches the minimum engine stop SoC value. When operating in SEVmode the prescribed increment amount is 3%. Other values are alsouseful.

Advantageously, the minimum engine stop SoC is higher when operating inthe SEV mode compared with the HEV mode. This allows longeruninterrupted periods of operation in EV mode in a number of situations.In the present embodiment the minimum engine stop SoC is around 43% whenoperating in HEV mode and around 44.5% when operating in SEV mode. Othervalues are also useful.

This feature has the advantage that a time period for which thepowertrain 131 operates in EV mode may be increased.

When the powertrain 131 is operated in a parallel mode, the controller140 is operable to assume the parallel torque boost mode when an amountof driver torque demand exceeds that which may be provided by the engine121 alone at its maximum torque output. As noted above, driver torquedemand is related to accelerator pedal position. In the SEV mode, thecontroller 140 limits provision of torque boost to situations in whichthe accelerator pedal is depressed more than a prescribed amount (whichmay be specified in terms of a proportion of full travel in someembodiments). In the present embodiment, when the vehicle is operated inthe SEV mode the parallel torque boost mode is only permitted when theaccelerator pedal 171 is depressed by more than 95%, corresponding tomovement of the pedal 171 beyond the ‘kick down’ detent in the presentembodiment. Other arrangements are also useful. However, this featureadvantageously reduces draining of charge from charge storage module 150relative to operation in the HEV hybrid operating mode.

In some embodiments the controller 140 may suspend provision of torqueboost in the SEV mode altogether.

Furthermore, the provision of torque filling is also restricted when inthe SEV mode compared with the HEV mode. In some embodiments torquefilling is not permitted in the SEV mode.

In some embodiments, energy overrun charging (i.e. use of the engine todrive the CIMG 123C in order to slow the vehicle when the engine 121 isswitched on) is not permitted in the HEV mode, but is permitted in theSEV mode. Other arrangements are also useful.

It is to be understood that the controller 140 is configured to storecomputer program code for causing one or more computing devices of thecontroller 140 to perform the method of vehicle control describedherein. It is to be understood that a controller according to anembodiment of the present invention may be provided by a plurality ofcomputing devices. The functionality described as being performed by thecontroller may be performed by a plurality of computing devices, controlmodules or the like, optionally at different physical locations of avehicle.

Embodiments of the present invention may be understood by reference tothe following numbered paragraphs:

-   1. A controller for a hybrid electric vehicle having an engine, an    electric propulsion motor powered by an energy storage device and an    electric generator operable to be driven by the engine to recharge    the energy storage device, the controller being operable to:    -   receive a signal indicative of a required hybrid operating mode        of the vehicle;    -   receive a signal indicative of a state of charge of the energy        storage device;    -   determine which of a plurality of powertrain modes is        appropriate for vehicle operation at a given moment, the        powertrain modes including an engine charging mode in which the        engine drives the generator to recharge the energy storage        device and an electric vehicle (EV) mode in which the engine is        switched off and the electric propulsion motor is operable to        develop drive torque to drive the vehicle; and    -   cause the powertrain to assume the appropriate powertrain mode        according to the required hybrid operating mode,    -   wherein the controller is operable to determine which of the        plurality of powertrain modes is appropriate for vehicle        operation in dependence at least in part on the signal        indicative of the instant state of charge of the energy storage        device and a reference value of state of charge, the controller        being operable to set the reference value of state of charge to        one of a plurality of different respective values in dependence        on the signal indicative of the required hybrid operating mode.-   2. A controller according to paragraph 1 operable to determine the    appropriate powertrain mode in dependence at least in part on a    deviation of the signal indicative of the instant state of charge    from the reference value of state of charge.-   3. A controller according to paragraph 1 operable to determine which    of the powertrain modes is appropriate at a given moment in time    according to a value of a cost function for each powertrain mode,    the value of the cost function being determined at least in part by    reference to the signal indicative of the instant state of charge    and the reference value of state of charge of the respective    powertrain modes.-   4. A controller according to paragraph 3 wherein the value of the    cost function of each powertrain mode is determined at least in part    in further dependence on at least one selected from amongst a rate    of fuel consumption of the vehicle, a rate of emission of a gas by    the vehicle and an amount of noise generated by the vehicle.-   5. A controller according to paragraph 4 configured to determine the    required powertrain mode according to a feedback Stackelberg    equilibrium control optimisation methodology.-   6. A controller according to paragraph 1 arranged to receive a    signal indicative of the required hybrid operating mode from a user.-   7. A controller according to paragraph 1 wherein the hybrid    operating modes include a first operating mode favouring prolonged    operation in EV mode, and a second operating mode favouring a    reduction in fuel consumption, wherein the value of reference state    of charge in the first operating mode is higher than that in the    second operating mode.-   8. A controller according to paragraph 7 wherein when the powertrain    is in the EV powertrain mode the controller is operable to cause the    powertrain to assume the engine charging powertrain mode in    dependence at least in part on driver torque demand, wherein when    the first mode is selected the controller is configured to cause the    vehicle to assume the engine charging powertrain mode only at higher    values of driver torque demand than when the second operating mode    is selected.-   9. A controller according to paragraph 7 wherein when the powertrain    is in the engine charging operating mode the controller is    configured to cause the generator to apply a greater charging load    to the engine when the vehicle is in the first operating mode    compared with the second operating mode.-   10. A controller according to paragraph 7 wherein the controller is    operable to cause the engine to switch on when vehicle speed exceeds    a prescribed value, the prescribed value being higher when the    vehicle is operating in the first mode relative to the second mode.-   11. A controller according to paragraph 10 wherein when the    controller causes the vehicle to operate in the first hybrid mode or    the second hybrid mode, the controller is arranged to cause the    engine to turn on in dependence at least in part on an amount by    which an accelerator pedal is depressed.-   12. A controller according to paragraph 7 wherein the state of    charge of the energy storage means is permitted to take a value from    a prescribed absolute minimum state of charge to a prescribed soft    minimum value greater than the prescribed absolute minimum state of    charge only when the vehicle is operating in the first hybrid    operating mode or upon vehicle initialisation.-   13. A controller according to paragraph 12 wherein the magnitude of    the interval from the prescribed absolute minimum state of charge to    the prescribed soft minimum value is approximately 10% of the    magnitude of the interval from the prescribed absolute minimum state    of charge to a prescribed absolute maximum state of charge.-   14. A controller according to paragraph 1 operable to cause the    engine to be drivably coupled to one or more wheels of the vehicle    in addition to the electric propulsion motor.-   15. A controller according to paragraph 14 operable to cause the    engine to deliver drive torque when the powertrain is operated in    the engine charging mode.-   16. A controller according to paragraph 14 operable to cause the    powertrain to operate in a parallel mode in which the engine    delivers drive torque to one or more wheels in addition to the    electric propulsion motor.-   17. A hybrid electric vehicle powertrain comprising a controller    according to paragraph 1.-   18. A powertrain according to paragraph 17 wherein the electric    generator and the electric propulsion motor are each provided by an    electric machine.-   19. A powertrain according to paragraph 18 wherein the controller is    operable to cause the electric machine to be operated as a    propulsion motor or as a generator. Optionally, a single electric    machine may be provided, performing the functions of a generator or    a propulsion motor as required.-   20. A powertrain according to paragraph 17 wherein the generator and    electric propulsion motor are provided by respective different    electric machines.-   21. A hybrid electric vehicle comprising a controller according to    paragraph 1 or a powertrain according to paragraph 15.-   22. A vehicle according to paragraph 21 operable in a parallel mode    in which the engine delivers drive torque to the powertrain.-   23. A vehicle according to paragraph 21 operable in a series mode in    which the engine drives the generator to develop charge to recharge    the battery or power the propulsion motor whilst the propulsion    motor delivers drive torque to the powertrain.-   24. A method of controlling a hybrid electric vehicle having an    engine, electric propulsion motor powered by an energy storage    device and an electric generator operable to be driven by the engine    to recharge the energy storage device, the method comprising:    -   receiving a signal indicative of a required hybrid operating        mode;    -   receiving a signal indicative of a state of charge of the energy        storage device;    -   determining which of a plurality of powertrain operating modes        is appropriate for vehicle operation at a given moment, the        powertrain operating modes including an engine charging mode in        which the engine drives the generator to recharge the energy        storage device and an electric vehicle (EV) mode in which the        engine is switched off and the electric propulsion motor is        operable to develop drive torque to drive the vehicle; and    -   causing the powertrain to assume the appropriate powertrain        operating mode and the required hybrid operating mode,    -   the method comprising determining which of the plurality of        powertrain operating modes is appropriate for vehicle operation        in dependence at least in part on the signal indicative of the        instant state of charge of the energy storage device and a        reference value of state of charge, and setting the reference        value of state of charge to one of a plurality of different        respective values in dependence on the signal indicative of the        required hybrid operating mode.-   25. A computer readable medium carrying computer program code for    controlling a vehicle to carry out the method of paragraph 24.

Throughout the description and claims of this specification, the words“comprise” and “contain” and variations of the words, for example“comprising” and “comprises”, means “including but not limited to”, andis not intended to (and does not) exclude other moieties, additives,components, integers or steps.

Throughout the description and claims of this specification, thesingular encompasses the plural unless the context otherwise requires.In particular, where the indefinite article is used, the specificationis to be understood as contemplating plurality as well as singularity,unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties orgroups described in conjunction with a particular aspect, embodiment orexample of the invention are to be understood to be applicable to anyother aspect, embodiment or example described herein unless incompatibletherewith.

1. A controller for a hybrid electric vehicle having a powertraincomprising an engine, an electric propulsion motor powered by a battery,and an electric generator operable to be driven by the engine torecharge the battery, the controller configured to: receive a signalindicative of a required hybrid operating mode of the vehicle; determinewhich of a plurality of powertrain modes is appropriate for vehicleoperation at a given moment, the powertrain modes including at least onepowertrain mode in which the engine is switched on and an electricvehicle (EV) powertrain mode in which the engine is switched off and theelectric propulsion motor is operable to develop drive torque to drivethe vehicle; and cause the powertrain to assume the appropriatepowertrain mode according to the required hybrid operating mode, whereinhybrid operating modes include a first hybrid operating mode favoringprolonged operation in the EV powertrain mode by promoting charging ofthe battery to a higher state of charge, and a second hybrid operatingmode favoring a reduction in fuel consumption, wherein the controller isoperable to cause the engine to switch on when vehicle speed exceeds aprescribed value, wherein the prescribed value when the vehicle isoperating in the first hybrid operating mode is set to a value exceedingthat of a prevailing speed limit of a road which the vehicle is drivingon.
 2. The controller of claim 1, configured to receive a signalindicative of the required hybrid operating mode from a user.
 3. Thecontroller of claim 1, wherein the prescribed value is higher when thevehicle is operating in the first hybrid operating mode relative to thesecond hybrid operating mode.
 4. The controller of claim 3, wherein theprescribed value in the first hybrid operating mode is 35 mph and theprescribed value in the second hybrid operating mode is 30 mph, theprevailing speed limit being 30 mph.
 5. The controller of claim 3,wherein the prescribed value in the first hybrid operating mode is 40mph and the prescribed value in the second hybrid operating mode is 35mph, the prevailing speed limit being 35 mph.
 6. The controller of claim1, wherein the controller is configured to receive a signal indicativeof a state of charge of the battery; wherein the powertrain modesinclude an engine charging mode in which the engine drives theelectrical generator to recharge the battery; wherein the first hybridoperating mode favors prolonged operation in the EV powertrain mode bypromoting charging of the battery to a higher state of charge when thepowertrain is in the engine charging mode; and wherein the controller isoperable for determining which of the plurality of powertrain modes isappropriate for vehicle operation in dependence at least in part on asignal indicative of an instant state of charge of the battery and areference value of state of charge, the reference value in the firsthybrid operating mode being higher than that in the second hybridoperating mode, and the controller being operable to set the referencevalue of state of charge to one of a plurality of defined respectivevalues in dependence on the signal indicative of the required hybridoperating mode and additionally in dependence on a selected transmissionmode, the selected transmission mode being one of a plurality ofselectable transmission modes.
 7. The controller of claim 6, configuredto determine the appropriate powertrain mode in dependence on adeviation of the signal indicative of the instant state of charge fromthe reference value of state of charge.
 8. The controller of claim 6,configured to determine which of the powertrain modes is appropriate ata given moment in time according to a value of a cost function for eachpowertrain mode, the value of the cost function being determined byreference to the signal indicative of the instant state of charge andthe reference value of state of charge of the respective powertrainmodes.
 9. The controller of claim 6, wherein the value of the costfunction of each powertrain mode is determined in further dependence onat least one selected from amongst a rate of fuel consumption of thevehicle, a rate of emission of a gas by the vehicle and an amount ofnoise generated by the vehicle, and wherein the controller is configuredto determine a required powertrain mode according to a feedbackStackelberg equilibrium control optimization methodology.
 10. Thecontroller of claim 6, wherein, when the powertrain is in the EVpowertrain mode, the controller is operable to cause the powertrain toassume the engine charging powertrain mode in dependence on drivertorque demand, wherein when the first hybrid operating mode is selectedthe controller is configured to cause the vehicle to assume the enginecharging powertrain mode only at higher values of driver torque demandthan when the second hybrid operating mode is selected.
 11. Thecontroller of claim 6, wherein, when the powertrain is in the enginecharging operating mode, the controller is configured to cause theelectric generator to apply a greater charging load to the engine whenthe vehicle is in the first hybrid operating mode compared with thesecond hybrid operating mode.
 12. The controller of claim 6, wherein thecontroller is configured to command the powertrain to assume the enginecharging mode when the second hybrid operating mode is selected and thestate of charge of the battery is below a prescribed soft minimum valuestate of charge, the soft minimum value state of charge being greaterthan a prescribed absolute minimum value state of charge, wherein thecontroller is configured to determine whether it is appropriate for thepowertrain to assume the engine charging powertrain mode or the EVpowertrain mode when the vehicle is operating in the first hybridoperating mode or upon vehicle initialization and the state of charge isbelow the prescribed soft minimum value state of charge, wherein amagnitude of an interval from the prescribed absolute minimum valuestate of charge to the prescribed soft minimum value state of charge isapproximately 10% of the magnitude of the interval from the prescribedabsolute minimum value state of charge to a prescribed absolute maximumvalue state of charge.
 13. The controller of claim 6, wherein if thestate of charge reaches a value below a prescribed engine start value ofthe state of charge, the controller commands the engine to start and thepowertrain to assume the engine charging mode until the state of chargeexceeds a prescribed minimum engine stop value of the state of charge,wherein once the state of charge exceeds the minimum engine stop valueof the state of charge the powertrain may resume operation in the EVpowertrain mode if the controller determines this is the optimumpowertrain mode according to an energy optimization strategy; andwherein if the powertrain resumes operation in the EV powertrain modeonce the state of charge exceeds the prescribed minimum engine stopvalue of the state of charge following an engine start due to the stateof charge falling below the engine start value of the state of chargecausing the powertrain to assume the engine charging mode, the minimumengine stop value of the state of charge is incremented by a prescribedincrement amount.
 14. A hybrid electric vehicle, comprising: apowertrain comprising an engine, an electric propulsion motor powered bya battery, an electric generator operable to be driven by the engine torecharge the battery, and a controller; wherein the controller isconfigured to: receive a signal indicative of a required hybridoperating mode of the vehicle; determine which of a plurality ofpowertrain modes is appropriate for vehicle operation at a given moment,the powertrain modes including at least one powertrain mode in which theengine is switched on and an electric vehicle (EV) powertrain mode inwhich the engine is switched off and the electric propulsion motor isoperable to develop drive torque to drive the vehicle; cause thepowertrain to assume the appropriate powertrain mode according to therequired hybrid operating mode, wherein hybrid operating modes include afirst hybrid operating mode favoring prolonged operation in the EVpowertrain mode by promoting charging of the battery to a higher stateof charge, and a second hybrid operating mode favoring a reduction infuel consumption; and cause the engine to switch on when vehicle speedexceeds a prescribed value, wherein the prescribed value when thevehicle is operating in the first hybrid operating mode is set to avalue exceeding that of a prevailing speed limit of a road which thevehicle is driving on.
 15. The vehicle of claim 14, wherein the electricgenerator and the electric propulsion motor are each provided by anelectric machine, and wherein the controller is further configured tocause the electric machine to be operated as the electric propulsionmotor or as the electric generator.
 16. The vehicle of claim 14, whereinthe electric generator and electric propulsion motor are provided byrespective different electric machines.
 17. The vehicle of claim 14,further configured to operate in a parallel mode in which the enginedelivers drive torque to the powertrain.
 18. The vehicle of claim 14,further configured to operate in a series mode in which the enginedrives the electric generator to develop charge to recharge the batteryor power the electric propulsion motor while the electric propulsionmotor delivers drive torque to the powertrain.
 19. A method ofcontrolling a hybrid electric vehicle having a powertrain comprising anengine, an electric propulsion motor powered by a battery, and anelectric generator configured to be driven by the engine to recharge thebattery, the method comprising: receiving a signal indicative of arequired hybrid operating mode; determining which of a plurality ofpowertrain operating modes is appropriate for vehicle operation at agiven moment, the powertrain operating modes including at least onepowertrain mode in which the engine is switched on and an electricvehicle (EV) mode in which the engine is switched off and the electricpropulsion motor is configured to develop drive torque to drive thevehicle; causing the powertrain to assume the appropriate powertrainoperating mode and the required hybrid operating mode, wherein hybridoperating modes include a first hybrid operating mode favoring prolongedoperation in the EV powertrain mode by promoting charging of the batteryto a higher state of charge, and a second hybrid operating mode favoringa reduction in fuel consumption; and causing the engine to switch onwhen vehicle speed exceeds a prescribed value, wherein the prescribedvalue when the vehicle is operating in the first hybrid operating modeis set to a value exceeding that of a prevailing speed limit of a roadwhich the vehicle is driving on.
 20. A computer readable medium carryingcomputer program code for controlling a vehicle to carry out the methodof claim 19.